WO2024079086A1

WO2024079086A1 - Method and device for separating carbon dioxide from a gas stream with heat recovery

Info

Publication number: WO2024079086A1
Application number: PCT/EP2023/077984
Authority: WO
Inventors: Alexander Benjamin ZAKHER; Adrian Nikolai KÄSER
Original assignee: TUM Carbon Removal Initiative e.V.
Priority date: 2022-10-12
Filing date: 2023-10-10
Publication date: 2024-04-18
Also published as: DE102022126569A1

Abstract

The invention relates to a method and a device for separating carbon dioxide from a gas stream, wherein the following steps are carried out: providing a sorbent in a gas stream, wherein the gas stream contains gaseous carbon dioxide; absorbing carbon dioxide from the gas stream using the sorbent; performing a regeneration process by desorbing at least a proportion of the carbon dioxide that has been absorbed by the sorbent, wherein a product gas containing or consisting of carbon dioxide is released from the sorbent; extracting at least a proportion of the gaseous carbon dioxide that is contained in the product gas; and performing a process for changing the state of aggregation of the extracted gaseous carbon dioxide, wherein the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide, wherein waste heat that is released during the process for changing the state of aggregation is absorbed by at least one heat pump system, and wherein the at least one heat pump system is used to introduce heat energy into the regeneration process in order to provide reaction heat for the desorption and/or in order to heat the sorbent.

Description

Method and device for separating carbon dioxide from a gas stream with heat recovery

The invention relates to a method for separating carbon dioxide from a gas stream and to a device and a system for separating carbon dioxide from a gas stream. The invention further relates to the use of a device and/or a system for separating carbon dioxide from a gas stream. The increased concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere contributes significantly to global warming due to the greenhouse effect. Various methods are known for reducing the emission of carbon dioxide in various processes and for reducing the concentration of carbon dioxide in the atmosphere, in particular methods for separating carbon dioxide from gas streams, for example from exhaust gases, from industrial exhaust gases or directly from the ambient air or the atmosphere. Carbon dioxide is also referred to as carbon dioxide. The terms carbon dioxide, carbon dioxide and CO2 are used synonymously here and below.

Processes for separating carbon dioxide directly from the ambient air are also referred to as “Direct Air Capture” (DAC). In such a process, a gas stream is typically generated from the ambient air using blowers, whereby part of the CO2 present in the gas stream is extracted from the gas stream using a separation device. In the separation device, typically sorbents are used that can absorb CO2 contained in the gas stream. By means of desorption, the CO2 previously absorbed by the sorbent can be released from the sorbent. This released CO2 can then be used, for example, to produce various products, such as synthetic fuels, or it can be stored for a short or long period of time, for example by means of permanent, typically underground, storage of the CO2, which can reduce the CG2 concentration in the atmosphere. Such processes are typically referred to as "Carbon Capture and Storage" (CCS) - or, in connection with DAC, also as "Direct Air Carbon Capture and Storage" (DACCS).

Recently, various DAC processes and DACCS processes have been developed that are based on different technological approaches. For example, DAC processes are known from the documents WO 2019/092127, WO 2019/092128 and US 7,314,847 B1 in which various materials are proposed for use as sorbents for absorbing carbon dioxide from gas streams, for example from gas streams generated in industrial plants or directly from the ambient air.

A major problem with known carbon dioxide capture processes is that the energy consumption for such processes is high, which means that the costs of capturing carbon dioxide, in particular the costs of capturing carbon dioxide from the ambient air, and typically also the costs of storage, are high. Due to the high costs and high energy consumption of such processes, as well as the currently low costs of carbon dioxide emissions, economic operation of DACCS plants on an industrial scale is often not possible.

The invention is therefore based on the object of providing an improved solution that addresses at least one of the problems mentioned. In particular, the object of the invention is to provide a solution that makes it possible to reduce the costs of separating carbon dioxide from a gas stream.

According to a first aspect, the object is achieved by a method according to claim 1. According to this, a method for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, is provided, which comprises the following steps: providing a sorbent in a gas stream, wherein the gas stream contains gaseous carbon dioxide, absorbing carbon dioxide from the gas stream by means of the sorbent, carrying out a regeneration process by desorption of at least a portion of the carbon dioxide absorbed by the sorbent, wherein a product gas which contains or consists of carbon dioxide is released from the sorbent, removing at least a portion of the gaseous carbon dioxide contained in the product gas.

According to the invention, a process for changing the state of aggregation of the extracted gaseous carbon dioxide is carried out, wherein the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide, wherein waste heat which is emitted during the implementation of the process for changing the state of aggregation is absorbed by at least one heat pump system and wherein thermal energy for providing reaction heat for the desorption and/or for heating the sorbent is introduced into the regeneration process by means of the at least one heat pump system.

The process steps are preferably carried out in the order given. However, a different order of the process steps is also possible.

A gas stream is understood to mean in particular a gas that flows, for example an air stream. The gas stream can in particular be an air stream with air from the environment. Ambient air is typically also referred to as air. The terms ambient air and air are therefore used synonymously here and below. The low-carbon dioxide air from which carbon dioxide has been separated is also referred to as air here and below. The gas stream can also be a gas stream from an industrial process or another process, for example from flue gas or exhaust gas.

The gas stream contains at least a proportion of gaseous carbon dioxide so that at least a portion of this carbon dioxide can be separated. The ambient air can, for example, contain 0.04 vol.% carbon dioxide.

The gas stream is brought into contact with the sorbent so that the sorbent can absorb carbon dioxide from the gas stream. Sorbents are used in particular in sorption processes for the selective separation of gases The sorbent is preferably brought into contact with the gas stream during the first phase of a pressure, temperature or humidity change process. The sorbent reacts with the gas to be sorbed. During a second phase of the change process, the previously sorbed gas is released again by changing parameters such as pressure, temperature and/or the influence of other chemicals.

The sorbent can in particular comprise several sorbent particles. The sorbent is understood to be a substance that can absorb and release the substance to be sorbed. Sorbents can also be referred to as sorbents or sorbents. Sorption is understood to be processes that lead to an enrichment of a substance within a phase or at an interface between two phases. Sorption can comprise absorption, i.e. an enrichment within a phase, and/or adsorption, i.e. an enrichment at an interface. Sorption can also comprise chemisorption, i.e. the binding and release of substances by means of reversible chemical reactions. The desorption reaction is endothermic, so when regenerating during the warm phase of the temperature change process, heat must be added in order to allow the reverse reaction to take place partially or completely.

The supply of thermal energy required for the desorption reaction can be achieved by means of thermal energy provided by the at least one heat pump system. The thermal energy provided can, for example, be used entirely for the desorption reaction, or, for example, partially for the desorption reaction and partially for preheating the sorbent. Taking up carbon dioxide by means of the sorbent is to be understood in particular as absorbing and/or chemisorption and/or adsorbing carbon dioxide by means of the sorbent. The sorbent can absorb or sorb gaseous carbon dioxide in particular by means of absorption and/or by means of chemisorption and/or by means of adsorption and release it again by means of desorption.

For the sorption of carbon dioxide by means of temperature and humidity change processes, amines, for example diethanolamine (DEA), or alkali carbonates, for example sodium carbonate or potassium carbonate, or also alkaline earth metal oxides/hydroxides, for example magnesium oxide/hydroxide and/or calcium oxide/hydroxide, can be used as sorbents. A regeneration process is understood to mean in particular a process for carrying out a desorption in which the gas absorbed by the sorbent is released again. The regeneration process preferably takes place in a desorption reactor, wherein the desorption reactor is designed in particular to enable desorption. When carrying out the regeneration process, in particular a desorption of at least a portion of the carbon dioxide absorbed by the sorbent takes place.

The product gas that is released comprises carbon dioxide. The concentration, i.e. the volume fraction, of the carbon dioxide in the product gas is in particular many times higher than the concentration, i.e. the volume fraction, of the carbon dioxide in the gas of the gas stream. Removing at least a portion of the gaseous carbon dioxide contained in the product gas is to be understood in particular as meaning that at least a portion of the carbon dioxide present in the product gas is removed. Removing at least a portion of the gaseous carbon dioxide contained in the product gas can also include removing the majority of the carbon dioxide contained in the product gas or all of the carbon dioxide contained in the product gas.

Preferably, the product gas is compressed before removing at least a portion of the gaseous carbon dioxide contained in the product gas.

When carrying out a process for changing the state of aggregation of the extracted gaseous carbon dioxide, the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide. During the conversion or during the conversion process, waste heat is generated, which is absorbed by the at least one heat pump system. This waste heat serves in particular as a heat source. The heat can then be raised to a higher temperature level and then used to provide reaction heat for the desorption and/or to heat the sorbent. In this way, heat energy can be introduced into the regeneration process, i.e. for the desorption, by means of the at least one heat pump system.

The at least one heat pump system preferably comprises one heat pump, particularly preferably several heat pumps. The at least one heat pump system preferably comprises at least one compressor and at least one coolant, such as water, carbon dioxide, hydrocarbons, fluoroolefins. Particularly preferably, the at least one heat pump system further comprises at least one heat exchanger.

The at least one heat pump system can also comprise an open heat pump circuit or be designed as an open heat pump circuit.

In a particularly preferred embodiment of the at least one heat pump system, the formation of product gas in the desorption reactor is the source of the working medium for the at least partially open heat pump system, wherein it is at least partially liquefied as it passes through the heat pump system.

In one possible design variant of a product gas liquefaction system with heat recovery, the creation of product gas in the desorption reactor fulfills the function of the evaporator and the product gas simultaneously also represents the working medium in an at least partially open heat pump system, whereby it is first compressed in a compressor, then releases heat in a heat exchanger to another heat pump system or directly to the desorption process (to heat the sorbent and/or to provide heat for the reaction) and is then at least partially liquefied by expansion, e.g. in a throttle. The non-liquefied portion of the gas can be fed back into the partially open circuit together with the product gas from the reactor.

The at least one heat pump system, and in particular the heat pump, is preferably designed to absorb thermal energy from a reservoir with a lower temperature, namely from the process for changing the state of aggregation, using drive energy and to transfer it, together with the drive energy, as heat to a system to be heated with a higher temperature, namely the desorption reactor.

In particular, the following steps are carried out: transferring waste heat released during the conversion of the extracted gaseous carbon dioxide into liquid carbon dioxide into a heat pump system, and providing reaction heat for the desorption and/or heating of the sorbent during the regeneration process by introducing thermal energy by means of the heat pump system. Process heat is used as a heat source for the heat pump system, whereby this process heat is provided in particular by producing liquid carbon dioxide and/or dry ice. The heat pump system can then supply heat to the sorbent in order to provide heat for desorption. The process heat is also referred to here as waste heat.

Changing the state of aggregation can in particular comprise converting gaseous carbon dioxide into liquid carbon dioxide. Preferably, changing the state of aggregation comprises converting liquid carbon dioxide into solid carbon dioxide. In particular, changing the state of aggregation can comprise converting gaseous carbon dioxide into liquid carbon dioxide and converting the liquid carbon dioxide into solid carbon dioxide.

Changing the state of aggregation can in particular comprise converting gaseous carbon dioxide into supercritical carbon dioxide. Changing the state of aggregation preferably comprises converting supercritical carbon dioxide into liquid carbon dioxide. Changing the state of aggregation preferably comprises converting liquid carbon dioxide into solid carbon dioxide. It is particularly preferred if changing the state of aggregation comprises converting gaseous carbon dioxide into supercritical carbon dioxide and converting the supercritical carbon dioxide into liquid carbon dioxide, and preferably converting the liquid carbon dioxide into solid carbon dioxide. The terms solid carbon dioxide and dry ice are used synonymously in this document. Supercritical carbon dioxide, which is also referred to as supercritical carbon dioxide, is to be understood in particular as carbon dioxide in a fluid state above its critical temperature and its critical pressure.

One advantage of such a method is that, compared to known methods, the method described here requires significantly less energy for the overall process of separating carbon dioxide and changing the state of aggregation of the carbon dioxide. Due to the lower energy consumption and in particular in conjunction with the use of renewable energies, the separation of carbon dioxide from gas streams, in particular from the ambient air, and the changing of the state of aggregation of the carbon dioxide is made possible in an economical manner using the method described here. A further advantage is that the process is particularly possible in conjunction with the efficient use of mechanical and/or electrical energy, as is the case in particular with systems for the use of renewable energies, such as wind turbines, photovoltaic systems, hydroelectric power plants, etc., which can often be operated particularly economically in remote locations. Since remote locations in particular are also particularly well suited to the operation of systems for separating carbon dioxide from the ambient air, this type of energy supply is particularly economical at suitable locations, with electricity prices sometimes being very low.

A further advantage is that the cooling and/or changing of the state of aggregation of the carbon dioxide and the heating of the sorbent can be carried out by means of a single heat pump system, whereby the heat pump system can have several heat pumps. The waste heat generated during cooling and/or changing of the state of aggregation can thus be used as a heat source for the heat pump system, which is then used to heat the sorbent to release the carbon dioxide from the sorbent.

Furthermore, the waste heat generated during cooling and/or when changing the state of aggregation can be used in part as a heat source for a first heat pump system, with which the sorbent is then heated to release the carbon dioxide from the sorbent, and wherein a further part of the waste heat generated is absorbed by a further heat pump system and fed to the preheating of the sorbent.

When liquefying CO2 and/or producing dry ice, it is common to use air or cooling water for process cooling, so that large air coolers or water cooling towers are required when using known liquefaction systems. With the method described here and the at least one heat pump system used therein, such air coolers or water cooling towers can be dispensed with and, in a particularly advantageous manner, even the waste heat that accrues during CO2 liquefaction and/or producing dry ice can be reused by using it for desorption using the at least one heat pump system.

A further advantage is that heat, especially waste heat or process heat from the change of state, does not have to be transferred via an intermediate medium or must be released directly into the environment and the heat transfer area required for heat transfer can be reduced overall, whereby less superheating of the coolant must take place for the heat transfer and thus exergy loss is reduced.

Furthermore, a heat pump that would otherwise be required to provide heat for the desorption process and which extracts heat from the environment can either be omitted or made significantly smaller.

According to a particularly preferred embodiment, the method comprises the step of storing the solid carbon dioxide produced by the process for changing the state of aggregation in the form of dry ice in a dry ice storage facility.

One challenge of CCS, and particularly of DACCS, is the safe and controllable storage of carbon dioxide. For example, it is generally difficult to ensure and prove the whereabouts of captured carbon dioxide, for example in the context of a CO2 certificate trading system that takes negative emissions into account. This is typically only inadequately possible for processes such as mineralization or the injection of carbon dioxide in deep geological layers, such as depleted gas fields, even when using complex geophysical data collection methods. Leaks can occur, for example, through cracks far away from the location of a deep borehole or only after a long time, and are therefore difficult to detect and hardly predictable.

An alternative to the storage methods used in known processes is the storage of carbon dioxide in the form of dry ice, i.e. in solid form, on the earth's surface.

A key advantage of storing carbon dioxide in a solid state on the earth's surface is its good accessibility. Fill levels in a storage facility can be measured directly. A visual inspection of the stored dry ice is possible, as is the relocation of the stored CO2 to other storage locations. It is also possible to provide larger quantities of carbon dioxide as a raw material for synthetic fuels or for carbon dioxide fertilization of plants, for example, because the carbon dioxide can be removed directly from a dry ice storage facility with little effort. It is particularly preferred that the method comprises: generating the gas stream, in particular in the form of a gas stream generated from the ambient air, preferably by means of at least one blower, wherein in particular the sorbent is brought into contact with the gas stream in a sorbent-air contact system. The gas stream can in particular be generated with one or more blowers. In the sorbent-air contact system, contact is then made possible between the generated gas stream and the sorbent, so that the sorbent can absorb carbon dioxide from the gas stream.

According to a particularly preferred embodiment, the method comprises the steps of: compressing the product gas and then removing heat from the compressed product gas, wherein this heat is at least partially introduced into the regeneration process to provide reaction heat for the desorption and/or to heat the sorbent, wherein preferably the product gas, after the heat removal, is expanded and partially condensed in the process.

It is particularly preferred that the method comprises: preheating the sorbent after the absorption of carbon dioxide from the gas stream by means of the sorbent, wherein sensible heat of the sorbent is absorbed by a heat recovery system after the regeneration process and wherein heat energy is supplied to the sorbent to be preheated by means of this heat recovery system in order to preheat the sorbent. The preheating can be carried out, for example, by means of a bulk material heat exchanger. Sensible heat of the sorbent can thus be used to preheat the sorbent that is to be preheated. Such a heat recovery system used for preheating the sorbent can in particular be a heat recovery system that is different from the at least one heat pump system that is used to heat the sorbent. This is therefore preferably an independent system circuit. The heat recovery system can have a heat pump. Preheating can also be carried out, for example, alternatively or additionally by means of a heat supply via a connection to the heat pump system.

It is particularly preferred that after carrying out the regeneration process, the sorbent is again exposed to the gas stream, in particular in the sorbent air contact system, in order to again absorb carbon dioxide from the gas stream. Preferably, the sorbent is recirculated in a repetitive cycle in which it first absorbs carbon dioxide from the gas stream, then it is regenerated, and the absorbed carbon dioxide is then released again by desorption.

It is particularly preferred that the sorbent is brought to a temperature of preferably at least 40 °C, particularly preferably in a range between 80 °C and 150 °C, in particular above 100 °C, and preferably at most 200 °C when carrying out the regeneration process.

It is particularly preferred that the removal of at least part of the gaseous carbon dioxide contained in the product gas comprises: cooling the product gas and condensing at least part of the water vapor contained in the product gas to water, and preferably separating the condensed water from the product gas, wherein preferably waste heat that arises during the cooling of the product gas and/or the condensation is absorbed by the at least one heat pump system and wherein thermal energy is introduced into the regeneration process by means of this at least one heat pump system to provide reaction heat for the desorption and/or for heating the sorbent. Preferably, the water vapor contained is predominantly or completely condensed. Preferably, the waste heat that arises during the cooling of the product gas and/or during the condensation of water is raised to a higher temperature level by means of a heat pump system and fed to the regeneration process for the desorption of the sorbent.

Preferably, one heat pump system is used. However, several heat pump systems can also be used, for example, one heat pump system using process heat that arises during the cooling of the product gas and/or condensation and another heat pump system using process heat that arises during the implementation of the process for changing the state of aggregation.

The product gas preferably comprises carbon dioxide and water. The product gas preferably comprises at least 2 vol.% gaseous carbon dioxide, particularly preferably at least 10 vol.% gaseous carbon dioxide, in particular up to 50 vol.% gaseous carbon dioxide, for example the product gas can comprise approximately 50 vol.% water vapor and approximately 50 vol.% gaseous carbon dioxide. A first cooling of the product gas takes place, for example, to a temperature between -20 °C and +50 °C, especially at +10 °C. The water vapor contained in the product is mainly condensed out.

The product gas can be cooled, particularly after compression to an increased pressure, to the condensation temperature corresponding to this pressure (“saturated steam”), whereby it should condense, i.e. become liquid. For example, condensation would take place at a pressure of approx. 35 bar at approx. 0 °C.

It is particularly preferred that, while carrying out the process for changing the state of aggregation of the extracted gaseous carbon dioxide, the carbon dioxide is cooled by means of the at least one heat pump system, whereby the temperature of the carbon dioxide is reduced and the state of aggregation of the carbon dioxide changes. In particular, the gaseous carbon dioxide is cooled down, whereby heat is extracted from the carbon dioxide. In particular, when converting the gaseous carbon dioxide into liquid carbon dioxide, process heat is provided by the phase transition. In addition or alternatively, a countercurrent heat exchanger with a cold carbon dioxide stream can also be used for cooling. Heat can also be released to the environment over large areas.

It is particularly preferred that the at least one heat pump system comprises a heat pump with a coolant, the coolant in particular comprising or consisting of one or more hydrocarbons, for example butane, and/or water and/or a working fluid based on hydrofluoroolefin (HFO), wherein the coolant is preferably compressed by means of a compressor. The coolant can, for example, be compressed to a pressure of, for example, 30 bar to 40 bar when using butane as the coolant, in particular to a pressure of approximately 36.7 bar. The coolant preferably permanently withstands a temperature of at least 80 °C, particularly preferably at least 120 °C, in particular at least 140 °C.

It is particularly preferred that carrying out the process for changing the state of aggregation of the extracted gaseous carbon dioxide comprises: compressing the extracted gaseous carbon dioxide, and/or liquefying the extracted, in particular compressed, gaseous carbon dioxide, and preferably cooling the liquefied carbon dioxide, in particular by means of the at least one heat pump system, with which heat energy is used to provide reaction heat for desorption and/or for heating and/or drying the sorbent is introduced into the regeneration process, and/or producing solid carbon dioxide in the form of dry ice, preferably from the liquefied carbon dioxide.

Preferably, the method comprises: compressing the product gas, and preferably cooling the product gas, in particular by means of the at least one heat pump system, with which thermal energy is introduced into the regeneration process to provide reaction heat for the desorption and/or to heat the sorbent.

Here and in the following, compaction is to be understood as preferably a multi-stage compaction process.

The extracted gaseous carbon dioxide can be compressed in particular by means of a CO2 compressor, whereby the carbon dioxide can be compressed, for example, to a pressure of at least 10 bar, preferably at least 20 bar and preferably at most 50 bar, in particular approximately 40 bar. The extracted, in particular compressed, gaseous carbon dioxide can be liquefied in particular by means of a CO2 liquefaction system, whereby the carbon dioxide is particularly preferably liquefied by cooling to approximately 0 °C and heat extraction by means of the at least one heat pump system. Cooling to lower temperatures can then be carried out in particular in a countercurrent heat exchanger, whereby the liquefied carbon dioxide in particular gives off the heat to carbon dioxide which is approximately -70 °C to approximately -78.5 °C cold and which is created during the formation of dry ice and possibly sublimates out of the dry ice storage. Liquefied carbon dioxide can also be cooled in particular by means of the at least one heat pump system. Dry ice can be produced in particular by expanding the pressure of liquid carbon dioxide with evaporation of a portion of the liquid carbon dioxide, for example by means of a dry ice production system, in particular by means of a pellet extruder or a throttle.

It is particularly preferred that the sorbent comprises at least one alkali carbonate, preferably several alkali carbonates, wherein the sorbent preferably contains at least 5% by weight of sodium hydrogen carbonate and/or at least 5% by weight of potassium hydrogen carbonate, wherein the sorbent is regenerated by means of heat supply, wherein preferably gaseous carbon dioxide and water vapor are released from the sorbent. Preferably only a small amount of water vapor is released. In a particularly preferred embodiment, the product gas is circulated in the desorption reactor or in exchange with a connected system, with water vapor being removed from it by means of a suitable drying agent.

In this case, ambient pressure or an overpressure relative to the ambient pressure is preferably provided as the pressure in the area of the sorbent, in particular by the pressure being created by escaping carbon dioxide and heating. If an overpressure is present, water that is bound or created by the desorption reaction cannot evaporate, or at least only partially, in a particularly preferred manner and remains predominantly bound in the sorbent, so that evaporation does not occur or only partially occurs and thus no additional heat has to be introduced for the evaporation of at least part of the water. The energy efficiency can thus be significantly improved in a particularly advantageous manner at high temperatures of over 100 °C and/or an overpressure relative to the ambient pressure.

It is particularly preferred that the liquefied carbon dioxide is cooled, preferably by means of a countercurrent heat exchanger, and then relaxed in a dry ice production system to a pressure in the range between 90% and 110% of the ambient pressure, wherein in particular a first portion of the liquid carbon dioxide is provided as dry ice and a second portion as gaseous carbon dioxide, which is returned and heated, preferably by means of the countercurrent heat exchanger, wherein preferably the heated gaseous carbon dioxide is fed to a compressor for compression.

It is particularly preferred that the method comprises collecting carbon dioxide sublimated in the dry ice storage facility, and preferably feeding the sublimated carbon dioxide into the countercurrent heat exchanger, and converting the sublimated carbon dioxide into dry ice and storing the dry ice in the dry ice storage facility. Preferably, the sublimated carbon dioxide is compressed by means of a compressor before being converted into dry ice.

By means of the countercurrent heat exchanger, it is possible to return sublimated carbon dioxide to the process, and this can be done in a particularly energy-efficient manner. Liquid carbon dioxide, for example carbon dioxide condensed from the sublimed carbon dioxide at 4 °C, can preferably be cooled in the countercurrent heat exchanger to a temperature at the triple point before it is expanded and partially converted into dry ice. The preferably still cold gas stream with sublimed carbon dioxide can also be fed in and heated, for example, to 4 °C, in particular before the carbon dioxide is compressed and liquefied.

In particular, the cooling of the dry ice storage facility can be improved by capturing the carbon dioxide that has sublimated out of the dry ice into gaseous carbon dioxide due to penetrating heat, optionally liquefying it, converting it into dry ice and ultimately storing it again as dry ice in the dry ice storage facility. The waste heat that arises when converting the gaseous carbon dioxide into liquid carbon dioxide or into dry ice is particularly preferably also fed back into the regeneration process by means of the at least one heat pump system. This makes it possible to achieve an improved energy efficiency of the process as a whole in a particularly advantageous manner.

According to a further aspect, the object mentioned at the outset is achieved by a device for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, comprising a sorbent-air contact system which is designed to generate a gas stream and to receive a sorbent, wherein in particular the sorbent can be arranged in a generated gas stream, a desorption reactor which is designed to carry out a regeneration process by desorbing at least part of the carbon dioxide absorbed by the sorbent in order to release a product gas which contains carbon dioxide or consists of it from the sorbent, wherein an aggregate state change system which is designed to carry out a process for changing the aggregate state of gaseous carbon dioxide contained in the product gas, wherein the gaseous carbon dioxide can be converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide by means of the aggregate state change system, at least one heat pump system which is designed to recover waste heat which is generated during the Carrying out the process for changing the state of aggregation, wherein the at least one heat pump system is designed to introduce heat energy for providing reaction heat for the desorption and/or for heating the sorbent into the regeneration process, wherein the Device is preferably designed to carry out the method described here.

Such a device is understood to mean in particular a DAC system or a DACCS system.

According to a further aspect, the object mentioned at the outset is achieved by a system for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, and for storing the separated carbon dioxide, comprising a device as described here and a dry ice storage device which is designed to store solid carbon dioxide generated by means of the device in the form of dry ice.

According to a further aspect, the object mentioned at the outset is achieved by using a device as described here and/or a system as described here for separating carbon dioxide from the ambient air surrounding the device and preferably for storing the separated carbon dioxide in the form of dry ice.

For the advantages, design variants and design details of the various aspects of the solutions described here and their respective possible further developments, reference is also made to the description of the corresponding features, details and advantages of the other aspects and their further developments.

Preferred embodiments are explained below purely by way of example with reference to the accompanying figures. They show:

Fig. 1 : a process diagram of an embodiment of a method for

Separating carbon dioxide from a gas stream;

Fig. 2: a schematic representation of a first embodiment of a

Process for separating carbon dioxide from a gas stream;

Fig. 3: a schematic representation of a second embodiment of a

Process for separating carbon dioxide from a gas stream. In the figures, identical or essentially functionally identical or similar elements are designated by the same reference numerals.

Fig. 1 shows a process diagram of an embodiment of a method for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air.

In Fig. 1, movements of gaseous substances are shown as dotted lines, movements of solids as dashed lines and movements of liquids as solid lines. The heat flows described in connection with Fig. 1 are shown as dotted lines.

By means of a sorbent-air contact system 1 in which a blower is present, a gas flow is generated from the ambient air by means of the blower. In the sorbent-air contact system, a sorbent, which preferably comprises a large number of sorbent particles, is brought into contact with the gas flow. The gas flow generated from the ambient air comprises, among other things, carbon dioxide and water. The sorbent absorbs gaseous carbon dioxide from the gas flow. When the sorbent has absorbed carbon dioxide, the sorbent is removed 71 from the sorbent-air contact system 1 and introduced 72 into a desorption reactor 3 via a preheating system 2 with a bulk material heat exchanger. The heat required for desorption is provided by means of a heat pump system 10. The regenerated sorbent is introduced from the desorption reactor 3 into a sorbent heat extraction system 11 for heat recovery 73, where it releases part of its contained heat indirectly via a gas stream and/or directly via contact with heat transfer surfaces 86 to the sorbent to be preheated. The partially cooled sorbent is then returned to the sorbent air contact system 1 74, where it is used again to absorb carbon dioxide.

During the desorption or regeneration of the sorbent, a product gas is released and fed into a CO2 processing system 4 for product gas cooling and water condensation 94. The product gas comprises gaseous carbon dioxide, nitrogen and water vapor, and in this case, for example, 50 vol.% carbon dioxide. In the embodiment described here, the product gas is cooled to 10 °C so that most of the water vapor condenses and can be removed from the system as liquid water. The heat 87 extracted from the product gas is fed to the Heat pump system 10. The carbon dioxide is then fed to a CO2 compressor 5 95.

In the next step, the pre-dried carbon dioxide is compressed in the CO2 compressor 5, in particular in a multi-stage process, to a pressure of approximately 40 bar and then fed into a CO2 liquefaction system 6 96. The carbon dioxide is cooled down to 5 °C by contact with a heat exchanger of the heat pump system 10 and thereby transfers heat 89 to the heat pump system 10.

Below a critical temperature of 31 °C, liquid carbon dioxide can be produced at the appropriate saturated vapor pressure. At a temperature of 5 °C, the carbon dioxide condenses at a pressure of approximately 39.6 bar. The heat 89 released during condensation is fed to the heat pump system 10.

In order to increase the temperature level of the recovered heat from 5 °C to over 100 °C, which is preferably required for desorption, a heat pump filled with coolant is used. In this embodiment, a heat pump system with a coolant that includes butane is used. The coolant evaporates at a temperature of approximately 0 °C and a pressure of approximately 1.032 bar. The coolant is compressed in the heat pump system by means of a compressor to a pressure of, for example, 36.7 bar. The heat absorbed at 0 °C is then released again at this pressure and a condensation temperature of 150 °C, with condensation taking place on the inside of pipes or tube bundles or tube coils or so-called “pillow-plate” modules. “Pillow-plate” modules are understood to be modules for heat exchangers that have a wavy or pillow-shaped surface. The tubes are part of a bulk material heat exchanger system in desorption reactor 3, so that the heat on the outside of the tubes is transferred to a sorbent at a temperature of approx. 135 °C and carbon dioxide and water can be desorbed from the sorbent.

The carbon dioxide liquefied in the liquefaction system 6 is led 61 to a countercurrent heat exchanger 7 and cooled by means of the countercurrent heat exchanger 7. The liquid carbon dioxide is then led to a dry ice production system, where it is expanded as it passes through a suitable throttle and is thereby partially converted into solid carbon dioxide and partially into gaseous carbon dioxide. The portion of solid carbon dioxide is led 63 to a dry ice storage 9. The portion of gaseous carbon dioxide is discharged as a cold gas stream 98 with a Temperature of approximately -78.5 °C is passed back through the counterflow heat exchanger 7 and heated. This gas flow is then also fed to the compressor 5 93.

In the dry ice storage facility 9, under certain conditions (in particular a pressure between atmospheric pressure and 1.1 bar in the gas phase and a temperature of approximately -78.5 °C), gaseous carbon dioxide is continuously produced in a sublimation process which is caused by the constant input of heat from the environment, since the environment is typically warmer than the dry ice storage facility. The sublimated carbon dioxide is collected and then fed to the countercurrent heat exchanger 7 99. This gas stream is then also fed 93 to the compressor 5, so that this sublimated carbon dioxide can first be used to produce liquid carbon dioxide and then solid carbon dioxide in the process described here, with the waste heat generated being fed back to the heat pump system 10.

Fig. 2 shows a first embodiment of a method 200 for separating carbon dioxide from a gas stream. The method is designed for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air. The method 200 comprises the following steps:

In a step 210, providing a sorbent in a gas stream, the gas stream containing gaseous carbon dioxide. In a step 220, absorbing carbon dioxide from the gas stream using the sorbent. In a step 230, carrying out a regeneration process by desorbing at least a portion of the carbon dioxide absorbed by the sorbent, a product gas containing or consisting of carbon dioxide being released from the sorbent. In a step 240, removing at least a portion of the gaseous carbon dioxide contained in the product gas. In a step 250, carrying out a process for changing the state of aggregation of the extracted gaseous carbon dioxide, wherein the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide, wherein waste heat which is emitted during the carrying out of the process for changing the state of aggregation is absorbed by at least one heat pump system and wherein heat energy for providing reaction heat for the desorption and/or for heating the sorbent is introduced into the regeneration process by means of the at least one heat pump system. Fig. 3 shows a second embodiment of a method 200 for separating carbon dioxide from a gas stream. The method is designed for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air. The method 200 comprises the following steps:

In a step 205, generating a gas stream, in particular in the form of a gas stream generated from the ambient air, preferably by means of at least one blower, wherein in particular the sorbent is brought into contact with the gas stream in a sorbent-air contact system. In a step 210, providing a sorbent in a gas stream, wherein the gas stream contains gaseous carbon dioxide. In a step 220, absorbing carbon dioxide from the gas stream by means of the sorbent. In a step 225, preheating the sorbent after absorbing carbon dioxide from the gas stream by means of the sorbent, wherein sensible heat of the sorbent is absorbed by a heat recovery system after the regeneration process and wherein thermal energy is supplied to the sorbent to be preheated by means of this heat recovery system in order to preheat the sorbent. In a step 230, performing a regeneration process by desorbing at least a portion of the carbon dioxide absorbed by the sorbent, wherein a product gas containing or consisting of carbon dioxide is released from the sorbent. After performing the regeneration process, the sorbent is exposed to the gas stream again, in particular in the sorbent-air contact system, to again absorb carbon dioxide from the gas stream. In a step 240, removing at least a portion of the gaseous carbon dioxide contained in the product gas. Removing at least a portion of the gaseous carbon dioxide contained in the product gas comprises: cooling the product gas and condensing at least a portion of the water vapor contained in the product gas to water, and preferably separating the condensed water from the product gas. Preferably, the waste heat that arises during the cooling of the product gas and/or the condensation is absorbed by the heat pump system and brought to a higher energy level, so that by means of the heat pump system, thermal energy can be introduced into the regeneration process to provide reaction heat for the desorption and/or to heat the sorbent. In a step 250, carrying out a process for changing the state of aggregation of the extracted gaseous carbon dioxide, wherein the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide, wherein waste heat that arises during the Carrying out the process for changing the state of aggregation, the carbon dioxide released during the process for changing the state of aggregation is absorbed by at least one heat pump system, and the at least one heat pump system is used to introduce thermal energy into the regeneration process to provide reaction heat for the desorption and/or for heating the sorbent. While the process for changing the state of aggregation of the extracted gaseous carbon dioxide is being carried out, the carbon dioxide is cooled by means of the heat pump system, the temperature of the carbon dioxide being reduced and the state of aggregation of the carbon dioxide changing. Carrying out the process for changing the state of aggregation of the extracted gaseous carbon dioxide comprises: compressing the extracted gaseous carbon dioxide, and liquefying the extracted, in particular compressed, gaseous carbon dioxide, and cooling the liquefied carbon dioxide, in particular by means of the heat pump system, with which thermal energy is introduced into the regeneration process to provide reaction heat for the desorption and/or for heating and/or for drying the sorbent. A large part of the process heat is accounted for in particular by the heat of condensation. The liquefied carbon dioxide is cooled by means of a countercurrent heat exchanger and then expanded to ambient pressure in a dry ice production system. A first portion of the liquid carbon dioxide is provided as dry ice and a second portion is provided as gaseous carbon dioxide, which is returned and heated by means of the countercurrent heat exchanger, the heated gaseous carbon dioxide being fed to a compressor for compressing the gaseous carbon dioxide. In a step 260, the solid carbon dioxide produced by means of the process for changing the state of aggregation is stored in the form of dry ice in a dry ice storage facility. In a step 265, carbon dioxide sublimated in the dry ice storage facility is collected and the sublimated carbon dioxide is fed to the countercurrent heat exchanger. In a step 266, the sublimated carbon dioxide is converted into dry ice and this dry ice is stored in the dry ice storage facility. List of reference symbols

Sorbent air contact system

2 Preheating system

3 Desorption reactor 4 CO2 upgrading system

5 CO2 compressors

6 CO2 liquefaction system

Counterflow heat exchanger

8 Dry ice production system 9 Dry ice storage

10 Heat pump systems

11 Sorbent heat removal system

100 Carbon dioxide capture and storage system

61 , 62 Movements of liquids 63, 71 , 72, 73, 74 Movements of solids

86, 87, 88, 89 Heat flows

93, 94, 95, 96, 98, 99 Movements of gaseous substances

200 processes for the capture of carbon dioxide

205 to 266 process steps

Claims

Claims Method (200) for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, comprising the following steps:

Providing (210) a sorbent in a gas stream, the gas stream containing gaseous carbon dioxide,

Collecting (220) carbon dioxide from the gas stream by means of the sorbent,

Carrying out (230) a regeneration process by desorption of at least a portion of the carbon dioxide absorbed by the sorbent, wherein a product gas containing or consisting of carbon dioxide is released from the sorbent,

Removing (240) at least a portion of the gaseous carbon dioxide contained in the product gas, characterized by

Carrying out (250) a process for changing the state of aggregation of the extracted gaseous carbon dioxide, wherein the extracted gaseous carbon dioxide is converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide, wherein waste heat which is emitted during the execution of the process for changing the state of aggregation is absorbed by at least one heat pump system (10) and wherein heat energy for providing reaction heat for the desorption and/or for heating the sorbent is introduced into the regeneration process by means of the at least one heat pump system (10).

2. Method according to the preceding claim, comprising

Storing (260) the solid carbon dioxide produced by the process for changing the state of aggregation in the form of dry ice in a dry ice storage facility (9).

3. Method according to at least one of the preceding claims, comprising

Generating (205) the gas stream, in particular in the form of a gas stream generated from the ambient air, preferably by means of at least one blower, wherein in particular the sorbent is brought into contact with the gas stream in a sorbent-air contact system (1).

4. Method according to at least one of the preceding claims, comprising

Compressing the product gas, and then

Removing heat from the compressed product gas, wherein this heat is at least partially introduced into the regeneration process to provide reaction heat for the desorption and/or to heat the sorbent, wherein preferably the product gas, after the heat removal, is expanded and partially condensed in the process.

5. Method according to at least one of the preceding claims, comprising

Preheating (225) the sorbent after the absorption of carbon dioxide from the gas stream by means of the sorbent, wherein sensible heat of the sorbent is absorbed by a heat recovery system (11) after the regeneration process and wherein by means of this heat recovery system (11) thermal energy is supplied to the sorbent to be preheated in order to preheat the sorbent.

6. Method according to at least one of the preceding claims, wherein after carrying out the regeneration process, the sorbent is again exposed to the gas stream, in particular in the sorbent air contact system (1), in order to again absorb carbon dioxide from the gas stream, and/or wherein the sorbent is brought to a temperature of preferably at least 40 °C, particularly preferably in a range between 80 °C and 150 °C, in particular above 100 °C, and preferably at most 200 °C when carrying out the regeneration process.

7. The method according to at least one of the preceding claims, wherein the removal (240) of at least a portion of the gaseous carbon dioxide contained in the product gas comprises:

Cooling the product gas and condensing at least a portion of the water vapor contained in the product gas to water, and preferably separating the condensed water from the product gas, wherein preferably waste heat that arises during the cooling of the product gas and/or the condensation is absorbed by the at least one heat pump system (10), and wherein thermal energy for providing reaction heat for the desorption and/or for heating the sorbent is introduced into the regeneration process by means of the at least one heat pump system (10), and/or wherein the method comprises: compressing the product gas, and preferably cooling the product gas, in particular by means of the at least one heat pump system, with which thermal energy for providing reaction heat for the desorption and/or for heating the sorbent is introduced into the regeneration process.

8. Method according to at least one of the preceding claims, wherein during the implementation of the process for changing the state of aggregation of the extracted gaseous carbon dioxide, the carbon dioxide is cooled by means of the at least one heat pump system (10), wherein the temperature of the Carbon dioxide is reduced and the state of aggregation of the carbon dioxide changes.

9. Method according to at least one of the preceding claims, wherein the at least one heat pump system (10) comprises a heat pump with a coolant, the coolant in particular comprising or consisting of one or more hydrocarbons, for example butane, and/or water and/or a working fluid based on hydrofluoroolefin (HFO), wherein the coolant is preferably compressed by means of a compressor, wherein the coolant preferably permanently withstands a temperature of at least 80 °C, particularly preferably at least 120 °C, in particular at least 140 °C.

10. The method according to at least one of the preceding claims, wherein carrying out (250) the process for changing the state of aggregation of the extracted gaseous carbon dioxide comprises:

Compressing the extracted gaseous carbon dioxide, and/or

Liquefying the extracted, in particular compressed, gaseous carbon dioxide, and preferably cooling the liquefied carbon dioxide, in particular by means of the at least one heat pump system (10), with which thermal energy is introduced into the regeneration process to provide reaction heat for the desorption and/or for heating and/or drying the sorbent, and/or

Production of solid carbon dioxide in the form of dry ice, preferably from the liquefied carbon dioxide.

11. Method according to at least one of the preceding claims, wherein the sorbent comprises at least one alkali carbonate, preferably several alkali carbonates, wherein the sorbent preferably contains at least 5% by weight of sodium hydrogen carbonate and/or at least 5% by weight of potassium hydrogen carbonate, wherein the sorbent is regenerated by means of heat supply, wherein preferably gaseous carbon dioxide and water vapor are released from the sorbent.

12. Method according to at least one of the preceding claims, wherein the liquefied carbon dioxide is cooled, preferably by means of a countercurrent heat exchanger (7), and then expanded in a dry ice production system (8) to a pressure in the range between 90% and 1 10% of the ambient pressure, wherein in particular a first portion of the liquid carbon dioxide is provided as dry ice and a second portion as gaseous carbon dioxide, which is returned and heated, preferably by means of the countercurrent heat exchanger (7), wherein preferably the heated gaseous carbon dioxide is fed to a compressor for compressing the gaseous carbon dioxide.

13. Method according to at least one of the preceding claims, comprising

Collecting (265) carbon dioxide sublimated in the dry ice storage (9), and preferably feeding the sublimated carbon dioxide into the countercurrent heat exchanger (7),

Converting (266) the sublimated carbon dioxide into dry ice and storing the dry ice in the dry ice storage facility (9).

14. Device for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, comprising a sorbent-air contact system (1) which is designed to generate a gas flow and to receive a sorbent, wherein in particular the sorbent can be arranged in a generated gas flow, a desorption reactor (3) which is designed to carry out a regeneration process by desorbing at least part of the carbon dioxide absorbed by the sorbent in order to release a product gas which contains or consists of carbon dioxide from the sorbent, characterized by a state change system which is designed to carry out a process for changing the state of aggregation of gaseous carbon dioxide contained in the product gas, wherein the gaseous carbon dioxide can be converted into liquid carbon dioxide and/or supercritical carbon dioxide and/or solid carbon dioxide by means of the state change system, at least one heat pump system (10) which is designed to absorb waste heat which is emitted during the implementation of the process for changing the state of aggregation, wherein the at least one heat pump system (10) is designed to use heat energy for Providing reaction heat for the desorption and/or for heating the sorbent in the regeneration process, wherein the device is preferably designed to carry out the method according to one of the preceding claims. System (100) for separating carbon dioxide from a gas stream, in particular from a gas stream generated from the ambient air, and for storing the separated carbon dioxide, comprising a device according to the preceding claim, a dry ice storage facility (9) which is designed to store solid carbon dioxide generated by means of the device in the form of dry ice. Use of a device according to claim 14 and/or a system according to the preceding claim for separating carbon dioxide from the ambient air surrounding the device and preferably for storing the separated carbon dioxide in the form of dry ice.